The subject matter disclosed herein relates to a system for determining torsional displacement of a rotating shaft, and, more specifically, to a system and method for determining movement of a power generation system shaft and/or targets during operation.
Some power plant systems, for example certain nuclear, simple cycle, and combined cycle power plant systems, employ turbines in their design and operation. Some of these turbines include shafts which during operation are rotated at high speeds to transfer torque about the turbine and power generation system (e.g., from prime drivers to generators). These shafts may have long axial dimensions relative to respective thicknesses/radial dimensions of the shaft. As a result of these long axial dimensions and the magnitude of the torque transferred, these shafts may experience torsional displacement which may cause a first end of any given shaft to be displaced/twisted, and/or radially shifted relative to a second end of the shaft during operation. In some power generation systems the power output of turbines may be determined by monitoring a set of targets disposed circumferentially about the shaft, the displacement of these targets relative to one another providing a measurement of the twist imposed on the shaft due to torque on the shaft. When errors caused by radial movement are eliminated, the angle of twist on the shaft can be determined and related to a calibration. As a result, known, controlled and measured forces are applied to the shaft, and a highly accurate measure of the associated power output of the turbine may be delivered. Employment of a method that includes disposing a plurality of sensors at each end about the shaft in communication with a set of a plurality of targets disposed about each end of the shaft allows determination of the aforementioned error in measurement due to radial motion of the shaft. However, these systems may not be able to monitor axial shaft movement and/or may not be able to determine the effects of the shaft movement on the accuracy of torque measurements. Additionally, if the targets are not parallel to a centerline of the shaft, the measurement may introduce another error into the measured angle of twist of the shaft which may limit process accuracy and thus reduce the accuracy of the torque and power output determinations.